In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. As a resist material which satisfies these conditions, a chemically amplified resist is used, which includes a base resin that exhibits a changed alkali solubility under action of acid and an acid generator that generates acid upon exposure.
The reaction scheme of a chemically amplified resist is as follows. Upon exposure, acid is generated from the acid generator, and the alkali solubility of the base resin is changed by the action of the generated acid. For example, a positive-type resist typically contains, as a base resin, a resin having acid dissociable, dissolution inhibiting groups which dissociate by action of acid generated from the acid generator. When acid acts on such a resin, the acid dissociable, dissolution inhibiting groups dissociate, and the alkali solubility of the resin is increased.
Generally, when a resist pattern is formed using a chemically amplified resist, a baking treatment (post exposure baking; hereafter, abbreviated as “PEB”) is conducted. By conducting PEB, diffusion of acid within the resist film and dissociation of the acid dissociable, dissolution inhibiting groups are promoted. As a result, a chemically amplified resist is capable of achieving an extremely high sensitivity, as compared to a conventional non-chemically amplified resist.
Currently, chemically amplified resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1). Further, as such acrylic resins, those which have a structural unit derived from (meth)acrylate ester having an aliphatic polycyclic group such as an adamantane skeleton at the ester portion are generally used, as they exhibit excellent transparency in the vicinity of 193 nm and excellent dry-etching resistance.
Further, for improving the lithography properties, those which have plurality of structural units are currently used as the base resin component of chemically amplified resists. For example, a positive resist has a structural unit containing an acid dissociable, dissolution inhibiting group which is dissociable under action of acid generated from the acid generator, and also has a structural unit containing a polar group such as a hydroxyl group, a structural unit containing a lactone structure, and the like. Especially, a structural unit containing a polar group is widely used, as it enhances the affinity of the resist for an alkali developing solution, and contributes to improvement in the resolution. For example, in an acrylic resin, a (meth)acrylate ester having a hydroxyl group-containing aliphatic polycyclic group at the ester portion, such as a structural unit derived from hydroxyadamantyl (meth)acrylate, is generally used.
Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-241385